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Abstract:

A scanning electron microscope includes a main scanning electron
microscope unit having an electron optical column and a sample chamber, a
controller over the main scanning electron microscope unit, a single
housing that houses both the main scanning electron microscope unit and
the controller, and a bottom plate disposed under the single housing, the
main scanning electron microscope unit and the controller. A first leg
member is attached to a bottom face of the bottom plate on a side of the
controller with a first opening hole provided through the bottom plate on
a side of the main scanning electron microscope unit, and a damper is
fixed to a bottom face of the main scanning electron microscope unit and
disposed through the first opening hole.

Claims:

1. A scanning electron microscope comprising, a main scanning electron
microscope unit including an electron optical column and a sample
chamber, a control means over the main scanning electron microscope unit,
a single housing that houses both the main scanning electron microscope
unit and the control means, a bottom plate disposed under the single
housing, the main scanning electron microscope unit and the control
means, a first leg member attached to a bottom face of the bottom plate
on a side of the control means, a first opening hole through the bottom
plate on a side of the main scanning electron microscope unit, and a
damper fixed to a bottom face of the main scanning electron microscope
unit and disposed through the first opening hole.

2. The scanning electron microscope as described in claim 1, wherein the
damper is disposed in a direct contact with an installation plane.

3. The scanning electron microscope as described in claim 1, further
comprising a second leg member disposed under the first opening hole, on
an inner face of which the damper fixed.

4. The scanning electron microscope as described in claim 1, further
comprising a following mechanism with which to have the main scanning
electron microscope unit follow the bottom plate moving or the single
housing moving.

5. The scanning electron microscope as described in claim 4, wherein the
following mechanism comprises a plate member that is fixed to the damper
and disposed on a side of an installation plane from the bottom plate and
apart from the bottom plate, a spring connecting the plate member with
the bottom plate, and fixing means to fix the spring with a bottom face
of the bottom plate and an upper face of the plate member.

6. The scanning electron microscope as described in claim 1, further
comprising a chassis having a second opening hole, the chaises disposed
above an upper surface of the bottom plate and a pin that is fixed to the
sample chamber and inserted into the second opening hole.

7. A scanning electron microscope comprising, a main scanning electron
microscope unit including an electron optical column and a sample
chamber, a control means over the main scanning electron microscope unit,
a single housing that houses both the main scanning electron microscope
unit and the control means, a bottom plate disposed under the single
housing, the main scanning electron microscope unit and the control
means, a first leg member attached to a bottom face of the bottom plate
on a side of the control means, a second leg member attached to a bottom
face of the bottom plate on a side of the main scanning electron
microscope unit and a damper fixed to a bottom face of the main scanning
electron microscope unit and disposed coaxially with the second leg
member.

8. The scanning electron microscope as described in claim 7, wherein the
damper is disposed through the first opening hole and fixed to an inner
wall face of the second leg member.

9. The scanning electron microscope as described in claim 7, wherein the
second leg member is a separate member from the bottom plate.

10. The scanning electron microscope as described in claim 7, wherein the
second leg member is integrally molded with the bottom plate.

11. The scanning electron microscope as described in claim 7, further
comprising a second leg member support attached onto a bottom face of the
second leg member.

12. The scanning electron microscope as described in claim 7, wherein at
least four of the dampers are attached on the bottom face of the main
scanning electron microscope unit and at least a couple of the first leg
members are attached on a bottom face of the bottom plate on a side of
the control means.

13. A scanning electron microscope comprising, a main scanning electron
microscope unit including an electron optical column and a sample
chamber. a control means over the main scanning electron microscope unit,
a single housing that houses both the main scanning electron microscope
unit and the control means, a bottom plate disposed under the main
scanning electron microscope unit and the control means, a plurality of
leg members attached on a bottom face of the bottom plate, wherein the
leg members of the plurality of leg members attached under the main
scanning electron microscope unit have a vibration absorbing property and
there are more of the leg members attached on a side of the scanning
electron microscope than those on a side of the control means.

14. The scanning electron microscope as described in claim 13, further
comprising a pair of thru holes through the bottom plate under the main
scanning electron microscope unit, the pair of thru holes being aligned
with a pair of the leg members and a plurality of dampers fixed on a
bottom face of the main scanning electron microscope unit, wherein each
of the plurality of dampers is disposed through one of the thru holes and
fixed on an inner wall face of one of the leg members and each of the leg
members has a vibration absorbing property.

Description:

FIELD OF THE INVENTION

[0001] The present invention relates to a vibration control technology for
scanning electron microscopes and especially for scanning electron
microscopes of a desktop type.

DESCRIPTION OF RELATED ART

[0002] The scanning electron microscope (SEM), which has been known to be
able to obtain a high magnification image on an object, is able to have
an electron beam converge on the object, scan the electron beam on the
object, detect electrons emitted from the object and display a scanning
electron image of the object on an image display device. The scanning
electron microscope needs several tens times as high a voltage as 1
kilo-volt to be able to generate an electron beam. Moreover the scanning
electron microscope needs to have an internal atmosphere that is kept
vacuumed to stabilize the generated electron beam. Accordingly the
scanning electron microscope is equipped with a high voltage generating
device, a vacuum pump and needs to have a pressure-proof structure and
tends to become usually a large apparatus and sometimes so large as to be
installed in a dedicated room. Therefore the scanning electron microscope
is generally a large sized one to be installed in a clean room or
measurement room. Furthermore the scanning electron microscope needs to
have a structure whose vibration is well controlled to prevent an
observed image of the object from being deteriorated.

[0003] A pressure-proof structure of the conventional scanning electron
microscope is shown in FIG. 2. The shown scanning electron microscope is
usually a very large sized apparatus and has a main scanning electron
microscope unit, a control device to control the main scanning electron
microscope unit and a monitor to display observed images, each of which
is installed on a separate mount. In the case of the structure shown in
FIG. 2, a main scanning electron microscope unit 205, which includes such
devices as an electron beam gun 201, a lens unit 203, a sample chamber
202 and a sample stage 204, is secured to a load plate 206 and a whole
apparatus inclusive of these devices and the load plate 206 is installed
on dampers 207 disposed on a first mount. Due to this structure, a
vibration is not easily transmitted from the floor to the main scanning
electron microscope unit 205.

[0004] A main pump 209 to vacuum an inside of the main scanning electron
microscope unit is connected to a lower portion of the sample chamber 202
and vacuums an inside of the sample chamber 202. An evacuation passage
from the main pump 209 is connected through a pipe 210 to the electron
beam gun 201 to vacuum an inside of the electron beam gun as well as an
inside of the lens unit 203. A vibration control damper 211 is installed
between the main pump 209 and the sample chamber 202. With this
structure, transmission of a vibration generated in the main pump is
reduced. The patent document 1 discloses a structure of this type.

[0005] The monitor 212 on which observed images are displayed is supported
on a second mount 213. Inside the second mount 213 are housed a control
section 214 for such devices as the main scanning electron microscope
unit 205 and a computer 215 to perform an image processing on observed
images displayed on the monitor 212. Cooling fans are usually attached to
the control section and the computer 215 and are vibration sources for
the main scanning electron microscope unit 205. Having the main pump 209
to be a vibration source supported on a mount and the control section 214
and the computer to be another vibration source supported on another
mount, the vibration to be transmitted to the main scanning electron
microscope unit 205 is reduced. As a result, clear observed images
without noises attributed to the vibrations are obtained.

[0006] Recently such a small sized scanning electron microscope apparatus
as to be installed and used on a table or a working table has been
promoted, as technologies for the small sized scanning electron
microscope have been developed. Since a scanning electron microscope of
this small sized type is installed on a table, the control section for
the main scanning electron microscope unit to be a vibration source and
the vacuum pump to be another vibration source have to be supported on a
single mount and usually can not be supported separately on mounts apart
from each other. In FIG. 3 is shown a structure example for a desktop
type scanning electron microscope in which both the control section for
the main scanning electron microscope unit and the vacuum pump are simply
installed in a single housing. The main scanning electron microscope unit
305 comprises an electron beam gun 301, a lens unit 303, a sample chamber
302 and a sample stage 304. The main scanning electron microscope unit
305 is secured to a bottom plate 312 that supports a whole apparatus and
vibration control dampers 313 are attached between the main scanning
electron microscope unit 305 and the bottom plate 312. The bottom plate
312 is supported by leg members 317. A main pump 309 to vacuum an inside
of the main scanning electron microscope unit is connected to an upper
portion of the lens unit 303 and a vibration control damper is attached
between the main pump 309 and the lens unit 303. A control unit 315
inclusive of a power supply and circuit boards is mounted on the bottom
plate 312 that supports the whole apparatus. In the control unit 315 is
installed such a devise as a cooling fan. The scanning electron
microscope unit inclusive of all of the electron beam gun 301, the lens
unit 303, the sample chamber 302 and the sample stage 304 and the control
unit are covered with a cover 316.

[0007] As has been explained, if all the units that constitute a scanning
electron microscope of a conventional type are installed in a single
housing, a vibration generated on the floor and a vibration generated by
the pump are absorbed usually by dampers.

[0009] Since the scanning electron microscope as shown in FIG. 3 has the
control unit 315 fixed to the bottom plate 312, a vibration that is
generated by the cooling fan and can not be controlled by the dampers 313
is transmitted to the main scanning electron microscope unit. As a
result, the observed images can be adversely affected by the transmitted
vibration.

[0010] The objective of the present invention is to bring into reality a
desktop type scanning electron microscope in which a control unit
inclusive of a main scanning electron microscope unit, an evacuation
unit, a power supply and a cooling fan is installed on a single bottom
plate and whose vibration reduction function is better than the scanning
electron microscope of the conventional desktop type.

Measure to Achieve the Objective

[0011] According to an aspect of the technical scope of the present
invention, a damper to support a main scanning electron microscope unit
is extended toward an installation plane and further below the bottom
plate which supports the main scanning electron microscope unit and a
control unit. To be more specific, an opening hole is bored through the
bottom plate and the damper is extended through the opening hole and
further below the opening hole. As a result, the vibration absorbing
property of the scanning electron microscope of the present invention
becomes higher than that of the conventional one. The damper may be made
in direct contact with an installation plane or in contact with some
support members disposed on the installation plane.

Effect of the Present Invention

[0012] Since a length of the damper of the scanning electron microscope of
the present invention is made longer, a natural frequency of the main
scanning electron microscope unit is lowered if the size (especially
height) of the main scanning electron microscope unit is unchanged from
that of the conventional scanning electron microscope. Accordingly a
vibration free frequency band becomes wider than the conventional one and
the vibration reduction property becomes better than the conventional
one.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 shows a vibration reduction structure of a scanning electron
microscope for the first embodiment.

[0016]FIG. 4 shows an internal structure of an electron optical column of
a scanning electron microscope for the first embodiment.

[0017]FIG. 5 shows a modified vibration structure of a scanning electron
microscope of the first embodiment.

[0018]FIG. 6 shows a vibration reduction structure of a scanning electron
microscope for the second embodiment.

[0019]FIG. 7 shows a plan view for a scanning electron microscope for the
second embodiment.

[0020]FIG. 8 shows a layout of a scanning electron microscope in which a
leg member does not function as a damper.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Hereinafter are explained embodiments.

First Embodiment

[0022] An explanation is given on a structure of a desktop type scanning
electron microscope in which a damper is in direct contact with a floor
surface through an opening hole bored through the bottom plate.

[0023] Firstly a structure of an electron scanning microscope is explained
with reference to FIG. 4. A main scanning electron microscope unit for
the present embodiment is constituted by such devices as an electron beam
gun 1, a lens unit 3 as a sample chamber 2. As is not shown in FIG. 4, a
sample stage is installed inside the sample chamber 2. When the apparatus
is being used, an inside of the apparatus is vacuumed to a vacuum level
higher than or equal to a predetermined vacuum level. When a high voltage
is applied to an electron source 17, an electron beam 18 is emitted.
Since the emitted electron beam 18 undergoes a convergence action from a
potential of a wehnelt electrode 19, the emitted electron beam 18
propagates along on a curved trajectory and a first crossover 21 is
formed between the wehnelt electrode 19 and an anode 20. The electron
beam 18 passes through the anode 20 while being accelerated by a voltage
difference between the wehnelt electrode 19 and the anode 20
(acceleration voltage) and undergoes a convergence action from a first
condenser lens 22. As a result, a second crossover 24 is formed between
the first condenser lens 22 and a second condenser lens 23. The electron
beam 18 undergoes a convergence action from the second condenser lens 23
after passing a position for the second crossover 24 and a third
crossover 26 is formed between the second condenser lens and an objective
lens 25. Since the electron beam 18 widened up to a predetermined size is
allowed to pass through an objective lens aperture 27 after the electron
beam 18 passes a position on the third crossover 26, only a part of the
electron beam 18 comes incident on the objective lens 25. The electron
beam 18 coming incident on the objective lens 25 converges on and
radiates to a surface of the sample stage 28. On the electron beam 18
radiating onto a surface of a sample, backscattered electrons flying from
on the surface of the sample are generated of the electron beam 18
radiating to the sample surface and secondary electrons flying from on
the surface of the sample are generated of the surface of the sample. A
detector, which is not shown, is installed in the sample chamber 2 and
has a function of detecting the backscattered electrons and the secondary
electrons and outputting detection signals. An image signal is made of
the detection signal after transmitted to an amplification circuit and an
AD conversion circuit and is further transmitted to a monitor, where an
image of the image signal is displayed. The quality of the displayed
image is influenced by such factors as the vibration of the apparatus,
noises and stains.

[0024]FIG. 1 is a cross sectional view for an entire structure of the
present embodiment. This desktop type scanning electron microscope of the
present embodiment comprises a main scanning electron microscope unit 5
which is inclusive of an electron beam gun 1, a lens unit 3, a sample
chamber 2 and a sample stage 4 and is installed on support members having
a vibration absorbing property and disposed on a floor on which the
apparatus is installed. The main scanning electron microscope unit 5 is
not installed on a bottom plate 12 which supports the entire apparatus.
To enable this structure, the bottom plate 12 has opening holes 108
through each of which a damper 13 is disposed on the floor surface. As is
not seen in FIG. 1, there are four dampers 13 attached on four corner
portions of the bottom plate 12 and the main scanning electron microscope
unit 5 is supported on the 4 points on an installation plane. The bottom
plate 12 is supported by leg members 106 on the installation plane.

[0025] A main pump 18 to evacuate and vacuum the inside of the main
scanning electron microscope unit 5 is connected to an upper portion of
the lens unit 3 through a damper 14 to absorb vibrations. On the bottom
plate 12 are installed a control unit 15 inclusive of a power supply for
the main scanning electron microscope unit 5 and the main pump 9, a
control circuit board and a cooling fan. The cooling fan is indispensable
for cooling the control unit 15 inclusive of the power supply and the
circuit board and the main pump 9. The main scanning electron microscope
unit 5 inclusive of the electron beam gun 1, the lens unit 3, the sample
chamber 2 and the sample stage 4 and the control unit 15 are covered with
a cover 16. The cover 16 is supported by the bottom plate 12 and disposed
not to be in contact with the main scanning electron microscope unit 5.

[0026] In the conventional structure shown in FIG. 3, there is no opening
hole corresponding to the opening hole 10B of the present embodiment and
all dampers 13 are disposed on the bottom plate 12. Accordingly the
length of the damper 13 is allowed to be made a length from the bottom
surface of the sample chamber 2 to the upper face 107 (indicated by a
single dashed line) of the bottom plate 12 at the largest in the
conventional structure. On the other hand, since the damper 13 is allowed
to extend lower than the upper face 107 toward the installation plane in
the present embodiment, it is possible to lower the natural vibration
frequency of the damper. As a result, the vibration free frequency band
is widened.

[0027] Another structural feature of the present embodiment is that
vibrations generated inside the apparatus are isolated from the damper 13
because the main scanning electron microscope unit 5 is separated from
the bottom plate 12 and supported directly by the installation surface.
Main vibration sources in the apparatus are the main pump 9 and the
cooling fan installed in the control unit 15. It is difficult to separate
the main pump 9 from the main scanning electron microscope unit 5 as the
inside of the main scanning electron microscope unit 5 has to be
vacuumed. However, the control unit 15 is allowed to be separated from
the main scanning electron microscope unit 5 except for its electrical
wire lines.

[0028] The control unit 15 that is one of the vibration sources is
possibly made to be a completely separate unit from the main scanning
electron microscope unit 5 as is shown in FIG. 2. However, in the case of
the desktop type scanning electron microscope in which the apparatus is
required to be made relatively small, the main scanning electron
microscope unit 5 and the control unit 15 are required to be housed
together in a single housing. Accordingly the structure of the present
embodiment works out for the desktop type scanning electron microscope.

Second Embodiment

[0029] In the case of the structure shown in FIG. 1, the vibration
reduction property is improved over the conventional structure because
the control unit 15 to be a vibration source is separated from the bottom
plate 12. However, since the main scanning electron microscope unit 5 is
not connected with the bottom plate 12 at all, the main scanning electron
microscope unit 5 can not follow the other parts of the total apparatus
that are moving and forced to be dragged when the total apparatus is
being moved. In case there is some impact applied to the apparatus, the
main scanning electron microscope unit 5 as well as the damper could leap
up onto the bottom plate 12. In the present embodiment, a following
mechanism to have the main scanning electron microscope unit follow the
bottom plate moving is additionally attached to get rid of the above
mentioned risk. Hereinafter a structure inclusive of this following
mechanism is to be explained.

[0030]FIG. 5 is an elevation view for a scanning electron microscope of
the present embodiment that is viewed from its sample chamber side (a
housing skipped and not shown). To have an explanation easily understood,
main structural elements are described with their sizes exaggerated and
as it is, each structural element is more or less as large as that
described in the scanning electron microscope in FIG. 1.

[0031] The following mechanism of the present embodiment has a feature of
generating a tension force with a spring exerted for following. Looking
at the structure in FIG. 5, it is seen that each of dampers 13 is divided
in two parts and that a plate member 31 is disposed inbetween.
Accordingly the plate member 31 is disposed under and apart from a bottom
plate 12. Instead of dividing each damper, a structure of having the
dampers disposed on the upper surface of the plate member 31 and second
leg members 500 disposed on the lower surface of the plate member 31 may
be used. Since the second leg member 500 is capable of being made to
slide smoothly on the floor, the second leg member 500 is made preferably
of such a material having a low friction coefficient as a fluorinated
carbon resin like fluorinated-poly-tetra-ethylene or Derlin (registered
trademark).

[0032] Springs 29 are disposed in a space between the bottom plate 12 and
the plate member 31. A pin 32 to fix one end of each of the springs 29 is
secured to the plate member 31. Moreover the other end of each of the
springs 29 is fixed to a pin 30 secured to a bottom surface of the bottom
plate 12. With these springs in place, a tension force is generated
between the bottom plate 12 and the damper 13 supporting the main
scanning electron microscope unit 5 and the main scanning electron
microscope unit 5 is capable of following the bottom plate 12 that is
moving. It should be understood that the pins 30, the pins 32 and the
springs 29 are disposed in such a way that a balanced position about
which the generated tension forces are balanced comes to a center or a
gravitational center of the sample chamber 2. Because the springs 29 are
kept balanced, each of the dampers 29 is centered in the opening hole 108
and kept off from the bottom plate 12. As a result, the vibration on the
bottom plate is prevented from being transmitted.

[0033] Though FIG. 5 shows the following mechanism in the left-right
direction on the page, it should be understood that there are pins and
springs disposed in the vertical direction to the page to generate a
tension force in the vertical direction for the following mechanism.
Accordingly tension forces are generated both in the X and Y direction,
which enable the scanning electron microscope to move while following the
apparatus.

[0034] In order to prevent the main scanning electron microscope unit 5
from running up onto the bottom plate 12, a flange 501 is formed on the
lower side of the sample chamber 2 and a pin 34 is further attached on
the flange 501. At the same time a chassis 35 is attached on the bottom
plate 12 to have the upper face of the chassis 35 face the flange 501.
There is a hole 36 in the chassis 35 through which the pin 34 stands. The
size of the hole 36 is such that the pin 34 is kept off from the chassis
35. With this structure used, the main scanning electron microscope unit
5 is stopped by the chassis 35 from leaping further up and running up
onto the bottom plate.

[0035] In the explanation on FIG. 5, the pin 34 is fixed to the flange 501
formed on the lower side of the sample chamber 2 and stand vertically to
the flange 501. However the pin may be fixed horizontally on the side
face of the sample chamber 2 and inserted in a hole in a plate member
standing vertically on the bottom plate 12. In this structure the flange
is not needed.

Third Embodiment

[0036] In the first embodiment an explanation is given on the structure of
the desktop type scanning electron microscope which has a damper in
direct contact with the floor surface. However there is problem with the
main scanning electron microscope unit following the bottom plate if the
damper is disposed simply on the apparatus installation plane. Therefore
the following mechanism as is used for the second embodiment is needed.
The present embodiment has a structure with which the damper is allowed
to be made longer than the conventional structure while there is not such
a problem with the following as for the first embodiment.

[0037] Firstly the vibration reduction structure of the present embodiment
is to be explained. The internal structure of the electron optical column
is the same as the first embodiment and its explanation is skipped.

[0038]FIG. 6 shows a cross section of the structure of a desktop type
scanning electron microscope of the present embodiment. A main scanning
electron microscope unit 606 inclusive of an electron beam gun 601, a
lens unit 602, a main evacuation pump 603, a sample chamber 605 and a
sample stage 605 is not fixed on a bottom plate 611 while only a control
unit 613 and a housing 610 are fixed on the bottom plate 611, which is
the same as the first embodiment. The main evacuation pump 603 to vacuum
an inside of the main scanning electron microscope unit 606 is connected
to an upper portion of the lens unit 602 through a buffer device 612 to
reduce vibration. The control unit 613 includes a electron optical column
(constituted by the electron beam gun 601 and the lens unit 602), a power
supply and a control circuit board for the main evacuation pump 603, and
a cooling fan. The main scanning electron microscope unit 606 and the
control unit 613 which are mentioned above are housed together in a
housing 614.

[0039] The scanning electron microscope 606 is supported by four vibration
reduction buffers 608. Here there are at least four opening holes 607
bored through the bottom plate 611 and the four vibration reduction
buffers 608 are disposed through the four opening holes 607. Moreover
there is a second leg member 609 disposed under each of the four opening
holes 607 and secured to the bottom plate with screws. A second leg
member support 629 is attached on the bottom of the second leg member
609. The second leg member support 629 is made of a material that
prevents a vibration from transmitting so that the main scanning electron
microscope unit 606 is not easily affected by an external vibration.

[0040] A significant feature of the present embodiment is that the
vibration reduction buffers 608 are not in direct contact with the floor
surface and are fixed to the second leg members 609 that are attached on
the back face of the bottom plate. Since an attachment surface of the
vibration reduction buffer 608 onto the second leg member 609 comes below
the bottom plate 611, the length of the vibration reduction buffer 608 is
allowed to be made longer than that for the conventional apparatus in
which the vibration reduction buffer 608 is disposed on an upper surface
of the bottom plate 611. In the case of the present embodiment, since the
vibration reduction buffer 608 is fixed on an inner wall surface of a
recess formed on the second leg member 609, the vibration reduction
buffer 608 is allowed to be made longer than that fixed on an upper
surface of the second leg member 609 that has no recess. Furthermore,
since the second leg member 609 is fixed to the bottom plate 611 and the
vibration reduction buffer 608 is fixed to the bottom plate 611, there is
no problem with the following.

[0041] Although the second leg member 609 is a separate member from the
bottom plate 611 and fixed to the bottom plate 611 with screws, it should
be obvious that the same effect as the present embodiment is created if
the second leg member 609 and a bottom plate 611 are integrally produced
by press-molding the bottom plate into the second leg member 609 that is
integrally formed with the bottom plate 611. However the second leg
member 609 is preferably a separate member from the bottom plate 611,
because an effect of internal vibration is reduced if the main scanning
electron microscope unit 606 is separable from the housing 10 though not
completely separate from the housing 10 that is a vibration source.

[0042] As is the case with the first embodiment, the internal vibration is
dispersed and transmitted to the installation surface in this embodiment.
That is, the internal vibration generated in the cooling fan or the like
is necessarily transmitted to the second leg members 609 through the
bottom plate 611 and a part of the internal vibration is transmitted to
the floor surface through the second leg member supports. The remainder
is transmitted to and dampens at the vibration reduction buffers 608, and
further transmitted to the main scanning electron microscope unit 606
inclusive of the electron beam gun 601, the lens unit 602, the main pump
603, the sample chamber 604 and the sample stage 605.

[0043] On the other hand, in the case of the structure of the conventional
desktop type scanning electron microscope shown in FIG. 3, the dampers
313 on which the main scanning electron microscope unit 303 is mounted
are fixed onto the bottom plate 312. Accordingly, the internal vibration
generated at the cooling fan is transmitted to the main scanning electron
microscope unit 303 through the bottom plate 312 and the dampers 313 and
the main scanning electron microscope unit 303 is more affected by the
vibration generated inside the apparatus, compared with the structure of
the present embodiment. Therefore, the structure of the present
embodiment is capable of reducing the effect from the vibration generated
inside the apparatus.

[0044] Moreover, the present embodiment allows the lower surface of the
main scanning electron microscope unit 606 that is fixed onto the upper
surface of the vibration reduction buffers 608 to be disposed lower than
if the main scanning electron microscope unit 606 is mounted on the
bottom plate 611. Accordingly a gravitational center of the apparatus of
the present embodiment is made lower than that of the conventional
apparatus. If there is no difference of the height of the main scanning
electron microscope unit 606 from the conventional apparatus, the height
of the housing 614 is made shorter than the conventional apparatus by the
height difference in the lower surface of the main scanning electron
microscope unit 606 fixed onto the upper surface of the vibration
reduction buffers 608.

[0045] Another significant feature of the scanning electron microscope
having a vibration reduction structure of the present embodiment is that
support points of the vibration reduction buffers supporting the main
scanning electron microscope unit are identical with support points of
leg members supporting the bottom plate. FIG. 7 and FIG. 8 show plan
views for lay-outs of the first leg members and the second leg members.
FIG. 7 corresponds to a lay-out in which the support points of the
vibration reduction buffers are identical with the support points of the
leg members supporting the bottom plate, while FIG. 8 corresponds to a
lay-out in which the support points of the vibration reduction buffers
are not identical with the support points of the leg members supporting
the bottom plate.

[0046] In FIG. 7, a rectangle indicated by a reference number 701
indicates the bottom plate 701, on which the electron optical column
including the electron beam gun and the sample chamber. The housing,
which is not shown, is fixed onto the bottom plate 701. A rectangle
indicated by a dotted line indicates a projection face of the bottom face
(more or less consisting of that of the sample chamber) of the main
scanning electron microscope unit projected on the bottom plate 701. A
sample bringing in and out face through which a sample is brought in and
out of the sample chamber is disposed on the front side of the sample
chamber (lower side on the figure). The electron optical column is
disposed at the reference number 702. The control unit is disposed on the
bottom plate 701 and opposite the main scanning electron microscope unit.
A reference number 706 indicates a cooling fan. A rectangle 705 is a
projection face of a control means projected on the bottom plate 701. The
main evacuation pump is disposed more or less over a center of the bottom
plate.

[0047] A pair of the first leg members 708 are disposed inside the
projection face 705 of the control means and across the width of the
bottom plate 701. Similarly a couple of pairs of the second leg members
707 are disposed inside a projection face 703 of the main scanning
electron microscope unit.

[0048] In a case sown in FIG. 8, first leg members 708 and second leg
members 707 are disposed at four corner portions of the bottom plate 701
and vibration reduction buffers, which are support members to absorb
vibration and to be necessarily disposed on a lower portion of the main
scanning electron microscope unit, interfere with leg members, because
the vibration reduction buffers extend down through the bottom plate to
the installation surface in the structure of the present invention. As a
result, the width of the sample chamber is restricted and can not be made
longer as shown in FIG. 8.

[0049] On the other hand, in the case of the present embodiment, each of
the vibration reduction buffers 608 is fixed on an axis on which a second
leg member 609 as is indicated with a single dotted line in FIG. 6. That
is, a position of the vibration reduction buffer 608 at which a load is
applied is identical within the installation plane of a scanning electron
microscope with a position of the second leg member 609 at which the load
is applied. Looking at FIG. 7, each of the vibration reduction buffers
608 is disposed at a position of a second leg member 707 and does not
interfere with any of the leg members. Therefore the width of the sample
chamber is allowed to be made as large as the whole width of the bottom
plate.

[0050] Furthermore, since the main scanning electron microscope unit is
heaviest among the units constituting the apparatus as exemplified in
each of the embodiments 1 to 3, a gravitational center position of the
whole apparatus on the bottom plate is on the side of the main scanning
electron microscope unit from the center of bottom plate (an intersection
between single dotted lines (in FIG. 7)). As a result, there are more leg
members on the side of the main scanning electron microscope unit than on
the side of the control unit in each of the embodiments. As is shown in
FIG. 7, there are a pair of the first leg members 708 disposed on the
side of the control unit and a couple of pairs of the second leg members
707 on the side of the main scanning electron microscope unit.
Accordingly loads applied to the leg members are more or less averaged.